This research will study the behavioral and physiological correlates of the agitation-depression reaction following maternal separation in group living pigtailed (M. nemestrina) monkey infants. Behavioral data will be collected from birth. When the animals are several months of age, they will be implanted with multichannel biotelemetry systems that transmit EOG, EKG, EMG, body temperature, and 3 channels of EEG. Physiological variables to be measured include heart rate and body temperature circadian rhythms, sleep patterns, EEG activity, and possibly, measurements of immune system function. Early behavioral development will be correlated with the reaction to maternal separation, and long term changes resultant from maternal separation will be identified. The agitation-depression reaction is thought to represent a valuable animal model of depression and/or bereavement. The data also will improve our understanding of the role of attachment bonds in the ontogeny and phylogeny of high primates.